Inhibitory mechanisms of ammonia addition on soot formation during n‑decane pyrolysis

Abstract

Soot formation during the imperfect combustion or pyrolysis of fuels is harmful to engine efficiency·NH3 has been proved to reduce soot emission effectively in flames. In this work, the effect of NH3 addition on soot inhibition during n-decane pyrolysis was systematically investigated from a theoretical principle. The MD simulations indicate that the coking phenomenon is weakened with the NH3 addition. Besides, the NH3 additives make the concentration peak of the dominant gas products lag. Thus, the concentrations of crucial precursors (acetylene and propargyl) are reduced by NH3 addition. Moreover, the NH3 additives can also influence the PAH growth process through the PAHs with N atoms (N-PAHs). Then, the chemical kinetic analysis shows that proper addition of NH3 additives can meet the heat absorption demand of fuel cracking. Furthermore, the mass fractions of PAHs and soot particles decrease with NH3 addition, which is consistent with the results from MD simulations. The formation of the main carbonitride species originates from the reaction of CH3 and C2H5 with NH2 followed by the dehydrogenation or C-C bond breaking reaction. The carbon source directly involved in the formation of soot particle will be reduced and the growth of the soot particle will be inhibited by preventing the formation of the key reactants, such as the acetylene molecule.